The present invention relates to a vehicular headlamp of a type including a discharge bulb. More particularly, the invention relates to a vehicular headlamp having a structure for mounting a lighting circuit case to the lamp body of the headlamp.
Recently, discharge bulbs have increasingly been employed as the light source for vehicular headlamps because of their capability for high luminance irradiation.
A vehicular headlamp employing a discharge bulb requires a lighting circuit to apply high voltage for lighting the bulb. Generally, the lighting circuit is mounted in a separate lighting circuit case which is mounted to the exterior of the lamp body. Such an arrangement as has been conventionally employed is shown in FIG. 12, wherein a lighting circuit case 102 is fixed to an outer wall 104a of a lamp body 104 with a screw.
In the case where the lighting circuit case 102 is mounted on the outside of the lamp body 104 as described above, the lighting circuit case 102 must be waterproof so as to protect the lighting circuit 106 mounted therein. For this reason, the conventional lighting circuit case 102 is formed as an entirely separate unit structure, which must be provided with a high sealing capability and in which spaces not occupied by circuit components and the like are completely filled with a potting material such as an epoxy resin. However, manufacturing a lighting circuit unit employing the aforementioned waterproof structure requires high material costs and a large amount of labor, and the lighting circuit unit significantly adds to the weight of the overall lamp unit.
In the case where the lighting circuit case 102 is fitted to the outside of the lamp body 104 as described above, a hole 104b is formed in the lamp body 104 to pass a high voltage cable 112 for connecting the lighting circuit 106 to a socket 110 for the discharge bulb 108. Therefore, it is necessary to adequately seal the hole 104b.
It is possible to provide a structure for mounting the lighting circuit case within the lamp body. Merely disposing the lighting circuit case within the lamp body, however, may lead to problems as discussed below.
In the lamp unit assembling process, the lighting circuit case must be mounted within the lamp body prior to the assembly of the reflector and lens. As a result, it is substantially impossible to remove the lighting circuit case thereafter. In case of failure of the lighting circuit, the lamp unit as a whole has to be replaced. Moreover, in case of failure of the lamp unit owing to accident, etc., the lighting circuit case cannot be readily extracted from the lamp unit for recycling. Also, in order to provide a suitable structure for mounting the lighting circuit case to the inside of the lamp body, the mold used in the molding process for producing the lamp body inevitably becomes very complicated.